1. Field of the Invention
The present invention relates to self-contained emergency lighting packs for use with fluorescent lamps or tubes in standard fluorescent fixtures in order to provide for the illumination of at least one fluorescent lamp during times of power outages.
2. Description of the Prior Art
A number of prior art patents deal with emergency lighting devices. These patents are set forth in Table I.
Although many of these patents deal with the activation of fluorescent lamps, none of these patents disclose or suggest any of the novel features of the present invention. Specifically, the emergency lighting fluorescent pack of the present invention is a self-contained pack which may be synergistically mounted in line with a fluorescent lamp or alongside a fluorescent lamp. It is not necessary, nor is it desirable, to mount the pack within the portion of the fluorescent fixture containing the ballast used to drive the lamps when utility AC power is present. By mounting to the exterior of the fluorescent fixture, lower ambient temperatures are encountered, thereby improving the operation and extending the life of the batteries.
None of the prior art patents disclose or suggest a self-contained emergency lighting fluorescent pack which may
TABLE I __________________________________________________________________________ Patent No. Inventor Title Date __________________________________________________________________________ 2,170,456 H.W. Lord Electric Discharge Apparatus 1939 2,401,555 F.C. De Reamer Lighting System for Tubular Lamps And Holders For Use Therein 1946 2541,033 J. Cates Circuits For Electric Discharge Lamps 1951 3,217,156 G.W. Sherwood Emergency Lighting System 1965 3,233,091 S. Hunt Portable Stand-By Emergency Light 1966 Unit 3,239,716 V.M. Brooks Safety Circuit For Sequence Start 1966 Ballast With Disconnect Switches In The Primary And Secondary Windings 3,336,472 W. Steinig Device For The Safety Lighting of Rooms 1967 or Open-Air Installations 3,448,335 B.F. Gregory et al High Frequency AC-DC Fluoroescent Lamp 1969 Driver Circuit 3,591,796 John S.N. Barker Emergency Electric Lighting Installations 1971 3,659,179 Barker et al Emergency Electric Lighting Units 1972 3,660,714 E.A. Chandler Emergency Lighting System 1972 3,684,891 R.L. Sieron Fail-Safe Solid-State Emergency Lighting 1972 Power Supply and Transfer Circuit 3,688,123 A.H.B. Walker Emergency Fluorescent Lighting Apparatus 1972 3,758,823 P.L. Jett et al Battery Powered Fluorescent Light 1973 3,906,243 R.R. Herzog Retrofit Emergency Lighting System 1975 3,912,969 K. Nakai et al Discharge Lamp Lighting Apparatus 1975 3,946,301 R.R. Love Direct Current to Alternating Current 1976 Electronic Inverter With Overload and Short-Circuit Protection Circuitry 3,975,660 F. Knobel et al Starterless Low-Voltage Fluorescent-Lamp 1976 Circuit Arrangements __________________________________________________________________________
be used in line with a standard fluorescent lamp. Thus, U.S. Pat. No. 3,336,472, Steinig, discloses a device for supplying emergency lighting which is installed within a fluorescent lighting fixture. The device is placed within an elongated housing similar to a fluorescent lamp and incorporates therein batteries, electronic circuitry, and a light source 10. Thus, this device is not used in line with a standard fluorescent lamp but is used in substitution of an entire lamp.
U.S. Pat. No. 2,401,555, De Reamer, discloses a holder for series-connected fluorescent lamps, the holders interposed between these series-connected lamps. These holders however do not embody electronic circuitry for driving these lamps during power outages and are primarily utilized for insuring the deenergization of the lighting system when any particular fluorescent lamp is not properly in place.
Finally, U.S. Pat. No. 3,659,179, Barker et al., discloses an emergency electric lighting unit which is mounted onto a main fluorescent lamp 15 so as to provide emergency power via auxiliary fluorescent lamp 16. This emergency lamp is not in line with the standard fluorescent lamp 15 but is merely added onto the standard lamp, unlike the present invention.
The present invention also incorporates a new element; namely, a safety cradle mounted to the fluorescent fixture so as to close a microswitch mounted within the cradle when the fluorescent lamp is properly installed within the fluorescent fixture. This safety cradle may be used in all mounting arrangements of one version of the present invention and insures that the electrical connections to all fluorescent lamps electrically associated with the lamp selected to be driven by the pack during power outages are de-energized until such time that the latter fluorescent lamp is properly installed. Another version of the pack for original equipment manufacturers, does not utilize a safety cradle. This electrical de-energization prevents any shock hazard from utility AC or the higher voltage emergency generated power when replacing the lamp driven by the emergency pack. The use of a safety cradle in conjunction with an emergency lighting fluorescent pack to insure the de-energization of the pack and the terminals to which the fluorescent lamps interconnect is not disclosed or suggested by any of the cited prior art. Thus, although U.S. Pat. No. 3,239,716, Brooks, discloses a safety circuit for a sequence start ballast having disconnect switches in the primary and secondary windings, the circuitry disclosed therein utilizes one of two fluorescent lamps as a circuit breaker with respect to the potential of the operating circuit. That is, the lamp displacement is utilized to render the starting circuit inoperative. The circuitry disclosed in Brooks does not utilize an external safety cradle having a switch making contact with the exterior of a fluorescent lamp so as to de-energize the circuitry when the lamp is misaligned.
U.S. Pat. No. 2,401,555, De Reamer, merely discloses the use of lamp holders 4 in conjunction with a series-connected fluorescent lighting system, the holders incorporating switch contact 33 and 34 to insure the de-energization of the fluorescent lamps when they all are not properly installed within these holders. Thus, these holders are connected in series with the fluorescent lamps unlike the present invention where the safety cradle switch contacts the exterior of a fluorescent lamp and does not make electrical connection therewith.
The emergency lighting fluorescent pack according to the present invention also incorporates a ferro-resonant transformer operating at a high frequency, typically 11 kilohertz, whose output characteristics match the power requirements of the driven fluorescent lamp. This high frequency sinusoidal voltage impressed upon the fluorescent lamp ensures lamp ignition without the necessity of heating the filaments found within the lamp. In normal operation, these filaments are heated in order to produce free electrons and thereby enable ignition of the fluorescent lamp at utility line voltages. By use of high frequency sinusoidal electrical power, the ferro-resonant transformer ignites the fluorescent lamp with a voltage of between 300 and 600 VRMS at a power output of approximately ten watts. In order to sustain ionization of the lamp, five watts of power at approximately 120 volts RMS is needed. Maintenance of 300 to 600 VRMS across the lamp would quickly destroy it. By use of the ferro-resonant transformer operating in the constant current portion of its operation curve, the desired maintainance of a fluorescent lamp ionization is obtained at a low power requirement; that is, at a low current level. Such would not be possible with a conventional transformer since in order to generate the ten watts of power at three to six hundred volts RMS would necessitate more than ten watts of output power by the secondary transformer if it were clamped to a voltage drop of approximately 120 VAC, that is, the normal operating voltage of the fluorescent lamp.
Although ferro-resonant transformers have been widely used in generating alternating current and for voltage regulation thereof, such applications have typically been in the fifty to sixty hertz range. Furthermore, such ferro-resonant transformers are normally only operated along the constant voltage portion of their operating curve rather than along the constant current portion of the curve. Thus, although U.S. Pat. No. 3,946,301, Love, discloses a direct DC-AC inverter utilizing a ferro-resonant transformer 88, this inverter is disclosed as operating in the low frequency range, typically sixty hertz.
Furthermore, although a number of the cited prior art patents are used in emergency fluorescent lighting devices operating at high frequency during their emergency mode, such devices do not use a ferro-resonant transformer as part of their operating circuitry. Thus, U.S. Pat. No. 3,684,891, Sieron, assigned to the present assignee, discloses a failsafe solid state emergency lighting power supply and transfer circuit for a fluorescent lamp which operates at a frequency of approximately ten kilohertz. However, the oscillator output transformer 42 is not of a ferro-resonant design. Similarly, U.S. Pat. No. 3,906,243, Herzog, discloses a retrofit emergency lighting system for fluorescent lamps which utilizes a three kilohertz inverter for supplying emergency power to the fluorescent lamps. The frequency of operation is defined as being in the range of 2.5 kilohertz to 4.0 kilohertz and utilizes a standard transformer having a primary winding 25 and a secondary winding 26 for supplying the power from the inverter 20 to the circuitry associated with driving the fluorescent lamp. Similarly, U.S. Pat. No. 3,448,335, Gregory et al., discloses a high frequency AC-DC fluorescent lamp driver circuit operating at a frequency of approximately five to twenty kilohertz utilizing a saturable core output transformer T1 in order to drive the fluorescent lamp.